No abstract

The present work was carried out to determine the characteristics and antibacterial activity of 7S and 11S globulins isolated from cowpea seed (Vigna unguiculata (L.) Walp.). The molecular mass of 7S globulin was demonstrated by SDS-PAGE bands to be of about 132, 129 and 95 kDa corresponding the α/, α and β subunits. The molecular mass of 11S globulin was demonstrated by SDS-PAGE bands to be existed between 28 and 52 kDa corresponding the basic and acidic subunits. The minimum inhibitory concentrations MICs of 7S and 11S globulins isolated from cowpea seed were determined against Gram positive bacteria viz: Listeria monocytogenes LMG 10470, Listeria ivanovii FLB 12, Staphylococcus aureus ATCC 25923 and Streptococcus pyogenes ATCC 19615, and Gram negative bacteria such as Klebsiella pneumonia ATCC 43816, Pseudomonas aeruginosa ATCC 26853, Escherichia coli ATCC 25922 and Salmonella ATCC 14028 using disc diffusion assay; they were showed to be in the range 10 to 200 µg/mL. Transmission electron microscope (TEM) examination of the protein-treated bacteria showed the antibacterial action of 11S globulin against S. typhimurium and P. aeruginosa was manifested by signs of cellular deformation, partial and complete lysis of cell components. Adding 11S globulin at both concentrations 50 and 100 µg/g to minced meat showed considerable decreases in bacterial counts of viable bacteria, psychrotrophs and coliforms compared to controls during 15 days storage at 4 °C, reflecting a promising perspective to use such globulin as a meat bio-preservative.

Native egg white protein with high level of acidic amino acid residues (pI = 4.8) and hydrophilic nature was transformed into its methylated derivative (MEW), acquiring rather hydrophobic and basic character (pI = 8). The MIC of MEW against ten studied bacteria (G+ and G−) ranged between 0.5 and 1 μg/disc matching or excelling the comparative values of some known specific antibiotics (ranging from 1 to 7.5 μg/disc). Combinations of MEW (1 MIC) and different ready-made disc concentrations of antibiotics indicated either nil, antagonistic or synergistic antimicrobial effect. Replacing the antibiotic Ciprofloxacin by gradual levels of MEW (20–100 %) proportionally increased the potentiality to induce bigger sized inhibition zones. MEW (1 MIC) could inhibit the growth of 6 G+ and 4 G− pathogenic bacteria in their liquid broth media during 24 h at 37 °C, indicating its broad and wide specificity. TEM examination indicated the susceptibility of the two types of bacteria (G+ and G−) to the antimicrobial action of MEW as manifested in different signs of cellular deformations, confirming its broad specificity and its mode of action was rather targeting the cell wall and cell membrane.

Crude, phenolic-rich extracts (CPREs) were isolated from different sources, such as Hibiscus sabdariffa (H. sabdariffa), Brassica oleracea var. capitata f. rubra (B. oleracea) and Beta vulgaris (B. vulgaris) and characterized. These CPREs showed potential antibacterial and antifungal activities. H. sabdariffa CPRE (HCPRE) is the most potent, as it inhibited all tested bacteria and fungi. Total anthocyanins content (TAC), total phenolic content (TPC) and total flavonoid content (TFC) were estimated in all three CPREs. H. sabdariffa contained 4.2 mg/100 g TAC, 2000 mg/100 g of TPC and 430 mg/100 g of TFC in a dry weight sample. GC–MS analysis of HCPRE showed 10 different active compounds that have antimicrobial effects against pathogenic bacteria and fungi, especially alcoholic compounds, triazine derivatives and esters. Scanning and transmission electron microscopy images of Staphylococcus aureus DSM 1104 and Klebsiella pneumonia ATCC 43816 treated with HCPRE (50 μg/mL) exhibited signs of asymmetric, wrinkled exterior surfaces, cell deformations and loss of cell shapes; and adherence of lysed cell content led to cell clumping, malformations, blisters, cell depressions and diminished cell numbers. This indicates death of bacterial cells and loss of cell contents. Aspergillus ochraceus EMCC516 (A. ochraceus, when treated with 100 μg/mL of HCPRE showed irregular cell organelles and cell vacuolation.